Archive for April, 2010

This is a list of papers on laboratory measurements of absorption properties of other GHGs than carbon dioxide (carbon dioxide has its own list). The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Studies of several gases and other general papers

The infrared absorption cross-section and refractive-index data in HITRAN – Massie & Goldman (2003)“The cross-sections and indices of refraction on the HIgh-resolution TRANsmission (HITRAN) database are summarized. HITRAN contains a tabulation of cross-sections of atmospheric chemical reservoir and source species, chlorofluorocarbons, hydrochlorofluorocarbons, and hydrofluorocarbons, and indices of refraction of liquid and solid compounds. The temperature and pressure dependences of the cross-sections and the temperature dependence of the indices of refraction are illustrated. Data uncertainties and applications are discussed, and some future needs of the remote-sensing community are identified.”

Cw cavity ring-down infrared absorption spectroscopy in pulsed supersonic jets: nitrous oxide and methane – Hippler & Quack (1999)“We introduce cw cavity ring-down spectroscopy (cw-CRDS) in pulsed supersonic jet expansions employing a tuneable near-infrared cw diode laser and a solenoid slit nozzle. The cavity is mode-matched to the laser wavelength during the gas pulses to achieve highest resolution and lowest noise level. The new technique is characterised by observing very weak rovibrational lines of the ν1+3ν3 combination band of nitrous oxide near 7780 cm−1 and the ν2+2ν3 combination band of methane near 7510 cm−1. We demonstrate the increased spectral resolution due to the reduced Doppler width of rovibrational transitions and the spectral simplification afforded by the rotational cooling.”

Water vapour

New studies of the visible and near‐infrared absorption by water vapour and some problems with the HITRAN database – Belmiloud et al. (2000)“New laboratory measurements and theoretical calculations of integrated line intensities for water vapour bands in the near‐infrared and visible (8500–15800 cm−1) are summarised. Band intensities derived from the new measured data show a systematic 6 to 26% increase compared to calculations using the HITRAN‐96 database. The recent corrections to the HITRAN database [Giver et al., J. Quant. Spectrosc. Radiat. Transfer, 66, 101–105, 2000] do not remove these discrepancies and the differences change to 6 to 38%. The new data is expected to substantially increase the calculated absorption of solar energy due to water vapour in climate models based on the HITRAN database.” [Full text]

Measurements of absorption coefficients of water vapor by means of an H2O laser in the far-infrared – Kempkens et al. (1979)“Absorption coefficients of water vapor were investigated for the frequency of a water vapor laser in the far-infrared (λ = 118.6 μm). The theoretical treatment of these coefficients was carried out assuming self-broadening of H2O and D2O rotational transitions as well as foreign gas broadening of these vapors by nitrogen. Comparing these theoretical values with the corresponding experimentally determined data it turns out that there must be an additional absorption mechanism due to HDO molecules, which in low concentration are contained in natural water and in the D2O available. Taking into account the absorption by HDO, the theoretical and experimental values show a good agreement. In addition, the absorption coefficients of H2O and D2O were measured for foreign gas broadening by hydrogen and argon.”

Total Absorptance of Water Vapor in the Near Infrared – Burch et al. (1963)“The total absorptance ∫ A{v)dv of water vapor in the vicinity of its vibration-rotation bands near 5332, 3700, and 1595 cm−1 has been determined as a function of absorber concentration w and equivalent pressure Pe for pure water vapor samples and samples of water vapor mixed with nitrogen. The present results, together with previously published results of Howard, Burch, and Williams, are presented in graphical form; logarithmic plots give ∫ A(v)dv for various values of Pe as a function of absorber concentration w. These plots may be used in estimating total absorptance of water vapor in any sample for which w and Pe are known, and they may be applied in atmospheric studies.”

Methane

The Intensities of Methane in the 3–5 μm Region Revisited – Féjard et al. (2000)“The analysis of the linestrengths of the infrared spectrum of methane (12 and 13) in the 3–5 μm region has been revisited on the basis of new measurements from Fourier transform spectra recorded at Kitt Peak under various optical densities. A simultaneous fit of these new data with previously reported tunable difference-frequency laser data has been done. An effective transition moment model in tensorial form up to the third order of approximation within the Pentad scheme has been used. The standard deviations achieved are very close to the experimental precision: 3 and 1.5%, respectively, for the two sets of data for the 12CH4 molecule, representing a substantial improvement with respect to earlier studies. The integrated bandstrengths obtained in the present work differ from previously reported values by factors ranging from −5 to +6%.” [Full text]

Determination of the ν4 band strength of 12CH4 from diode laser line strength measurements – Jennings & Robiette (1982)“The strengths of over 50 lines in the ν4 region of 12CH4 were measured using a diode laser spectrometer. Forty-nine lines were assigned to transitions of the ν4 band. Analysis of the strengths of these 49 lines leads to a value of the integrated band strength S40 = 127 ± 4 cm-2 atm-1 at 295.7 K; this value is compared to other recent band strength determinations. The Herman-Wallis factor, expressing the dependence of the transition moment on rotational quantum number, is also discussed.”

Line positions and strengths of methane in the 2862 to 3000 cm−1 region – Toth et al. (1977)“Measurements of line center positions and strengths of 1591 absorptions of CH4 in the 2862 to 3000 cm−1 region have been made at high resolution. New assignments have been determined for several components in the P14 and P15 manifolds of the ν3 band of 12CH4. The strength data of the allowed transitions in the ν3 band have been analyzed to determine the band strength and the coefficients of the F factor. The strength data given by Pine (1976) were also included in the analysis. For the ν3 band, a strength of 259.5 cm−2 atm−1 at 296 K was obtained. Many forbidden lines in the ν3 band were also observed in the spectra Line strengths in the ν3 band of 13CH4 were determined from the spectra.”

Total Absorptance of Carbon Monoxide and Methane in the Infrared – Burch & Williams (1962)“The total absorptance ∫ A(v)dv of the major infrared bands of carbon monoxide and methane has been measured as functions of absorber concentration w and equivalent pressure Pe over wide ranges of these variables. The experimental results are presented graphically, and empirical equations relating ∫ A(v)dv, w, and Pe are presented. By employing small values of w and large values of Pe, it has been possible to determine the band strengths or intensities ∫ k(v)dv for the fundamental band of carbon monoxide and for v2, v3, and v4 fundamentals of methane; the values obtained are compared with results of other investigators.”

Ozone

The infrared spectrum of ozone – McCaa & Shaw (1968)“Fourteen bands of ozone between 500 and 3300 cm−1 have been identifiedand values of the vibrational anharmonic constants determined. The integrated band absorptances of many of these bands have been measured from spectra of a 32-m path of ozone-oxygen mixtures containing up to 30 atm cm O3 near 25°C. The dependences of the band absorptances on O3 concentration and total pressure are described and the strengths of nine of the bands are given. It is shown that the statistical band model describes the behavior of the bands reasonably well for the ranges of experimental variables used.”

Nitrous oxide

Total Absorptance by Nitrous Oxide Bands in the Infrared – Burch & Williams (1962)“The total absorptances of the 2563, 2461, 2224, 1285, 1167, 692, and 589 cm−1 bands of pure N2O and N2O mixed with N2 have been determined as a function of absorber concentration w and equivalent pressure Pe which involves the partial pressures of the two gases. The results are given in graphical form. In general, it is found that in situations in which existing theory predicts absorptance proportional to the square roots of pressure and absorber concentration, the total absorptance is indeed nearly proportional to the square root of absorber concentration but not to the square root of the pressure; for the 2224 cm−1 band, ∫ A(ν)dν α Pe0.37. In addition to graphical presentation of results, it is possible to express ∫ A{ν)dν in terms of w and Pe by means of empirical equations applicable to certain definite ranges of the variables; the validity and the limitations of such empirical equations are discussed. For samples for which the product of the absorption coefficient k(ν) and the absorber concentration is much less than unity for all frequencies in an absorption band, it is possible to measure the band intensity or band strength ∫ k(ν)dν. Values of band intensity for the 2563, 2461, 2224, 1167, and 589 cm−1 N2O bands are listed and compared with values previously reported by others.”

CFC’s, HCFC’s, and HFC’s

Thermal infrared cross-sections of C2F6 at atmospheric temperatures – Zou et al. (2004)“Spectral absorption cross-sections, kν (cm-1 atm-1), have been measured in the 8.0 and 8.95 μm bands of C2F6. Temperature and total (N2-broadening) pressure have been varied to represent the conditions specified in various models of the terrestrial atmosphere so that the absorption cross-sections can be applied directly to the optical remote-sensing of C2F6 in the atmosphere. The measured absolute intensities of the 8.0 and the 8.95 μm bands are (1.636±0.003)×10-16 and (0.467±0.0018)×10-16 cmmolecule-1, respectively.”

Absorption cross-sections of HFC-134a in the spectral region between 7 and 12 μm – Nemtchinov & Varanasi (2004)“Spectral absorption cross-sections kν (cm2 molecule-1) were measured in the 7.07, 8.08, 9.24, 10.3, and 11.9 μm bands of HFC-134a at temperatures between 190 and 296 K and pressures between 10 and 1013 hPa with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures and temperatures that characterise several of the commonly adapted model atmospheres, represent tangent heights in solar-occultation-type remote-sensing observations of the atmosphere, and the conditions recorded in atmospheric observations at Arctic latitudes. The integrated cross-sections (or integrated intensities) of the absorption bands in the 7.07, 8.08, 9.24, 10.3, and 11.9 μm regions are, in the unit of 10-17 cmmolecule-1, 0.4674, 9.711, 1.508, 0.8753, and 0.2527, respectively.”

Thermal infrared absorption cross-sections of CF4 for atmospheric applications – Nemtchinov & Varanasi (2003)“Spectral absorption cross-sections, kν (cm2 molecule−1), have been measured in the 7.8 μm band of CF4 at temperatures between 180 and 296 K and pressures between 10 and 1013 mb (hPa) with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures and temperatures that parameterize several of the commonly adapted model atmospheres, represent tangent heights in solar-occultation type remote-sensing observations of the atmosphere, and the conditions recorded in atmospheric observations at polar latitudes. The combined absolute intensity of all of the bands contributing to the absorption around 7.8 μm is (1.926±0.012)×10−16 cmmolecule−1.”

Laboratory technique for the measurement of thermal-emission spectra of greenhouse gases: CFC-12 – Evans & Puckrin (1996)“A new technique has been developed to make possible the laboratory study of the infrared-emission spectra of gases of atmospheric interest. The thermal-emission spectra are in local thermodynamic equilibrium, just as they are in the atmosphere, and are not chemiluminescent. Demonstration results obtained by the use of this new technique are presented for dichlorodifluoromethane (CFC-12) at a pressure of 0.5 Torr in a cell with a path length of 5 cm. The measured cell spectra have been compared with simulations with the FASCD3P radiation code. The measurements of the emission spectra of radiatively active gases may be important for the atmospheric greenhouse effect and global warming.”

Thermal infrared absorption coefficients of CFC-12 at atmospheric conditions – Varanasi & Nemtchinov (1994)“Spectral absorption coefficients kν (cm-1 atm-1) have been measured in the 9 and 11 μm bands of CFC-12 (CF2Cl2) using a high-resolution Fourier transform spectrometer. Temperature and total (broadening) pressure have been varied to obtain results at conditions representative of tropospheric and stratospheric layers of the atmosphere. The measured absolute intensities (in units of 10-17 cm.molecule-1) of the 9 and 11 μm bands are 7.595 ±0.070 and 5.750 ±0.068, respectively.”

Other greenhouse gases

Thermal infrared absorption cross-sections of CCl4 needed for atmospheric remote sensing – Nemtchinov & Varanasi (2003)“Highly accurate spectral absorption cross-sections kν (cm2 molecule−1) were in the 12.7 μm band of CCl4 at temperatures between 208 and 296 K and pressures between 10 and 1013 mb with a high-resolution Fourier-transform spectrometer. Our data were obtained at pressures p and temperatures T that characterize the atmospheric layers in the commonly adapted models of the atmosphere. The selected (p,T) combinations also represent tangent heights in solar-occultation-type remote sensing observations and actual conditions recorded by balloon-borne instruments in the Arctic. The combined absolute intensity (or integrated cross-section) of the bands contributing to the absorption around 12.7 μm is 6.295±0.102×10−17 cmmolecule−1.”

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In last few years there has been some studies where climate system feedback has been tried to determine from short-term measurements of surface temperature and outgoing radiation. They have studied what happens to the radiation leaving the Earth when surface temperature changes. Such studies have been Forster & Gregory (2006), Spencer et al. (2007), Spencer & Braswell (2008, 2009) and Lindzen & Choi (2009). Of these, teams of Spencer and Lindzen have found negative values for the feedback against common understanding (negative value of feedback would mean that the total warming effect from carbon dioxide would be small).

In a new study, Lin et al. (2010a) have looked into this and they focus especially to checking the results of Spencer & Braswell (2009, SB09). This new study hasn’t been officially published yet but it has been peer-reviewed and it is in press to be published in near future. Lin et al. use basically the same modelling and analysis methods as SB09, but Lin et al. include more realistic climate system which also includes climate “memory”. They refer to their earlier study (Lin et al., 2010b) where they studied the climate memory with climate feedback and found a positive feedback, and they also found that the feedback is more positive if the climate memory is longer.

First Lin et al. perform their modelling and analysis without climate memory and using the same feedback parameter value as SB09 to see if they can replicate the results of SB09. They do get the same result as SB09. Next Lin et al. perform the same analysis but now they include a one year memory to the climate system. In their earlier study they had found that climate memory is at least about 8 years. Now they use a one year memory because they wish to show that the total feedback of the climate system does not show up with quick surface temperature changes, even if there would be a short memory in the system. They already studied longer memories in their earlier study and found a positive feedback. Now they use one year memory and they then use different values for the feedback parameter from the extremely small value used in SB09 to bigger values. They find that the climate feedback with this short, one year climate memory, varies from very negative to slightly positive. They say:

During a short time period, there could be significant global surface temperature fluctuations. But the averaged temperature change during this period should be small. Thus, long-term feedbacks would be significantly weaker compared to short-term feedbacks during this period and cannot be detected by short-term observations.

They think that in order to determine the climate system feedback, one must use long-term observations and model runs. If an analysis uses only short-term observations and model runs, it may produce a feedback value that is significantly in error. In a short-term analysis it is likely to happen that the long-term response in the climate system determined by the climate memories cannot be seen from the noise of the fast climate processes. From Lin et al. new study, it seems that SB09 and other short-term studies have been measuring this noise.

Thanks to Tuomas for material supply and AJ for commenting the text and the subject.

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This is a list of papers on the atmospheric concentration of nitrous oxide (N2O) – one of the more important greenhouse gases. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Atmospheric nitrous oxide: patterns of global change during recent decades and centuries – Khalil et al. (2002)“Data from weekly global measurements of nitrous oxide from 1981 to the end of 1996 are presented. The results show that there is more N2O in the northern hemisphere by about 0.7 plus or minus 0.04 ppbv, and the Arctic to Antarctic difference is about 1.2 plus or minus 0.1 ppbv. Concentrations at locations influenced by continental air are higher than at marine sites, showing the existence of large land-based emissions. For the period studied, N2O increased at an average rate of about 0.6 ppbv/year (AA0.2%/year) although there were periods when the rates were substantially different.”

Variations in atmospheric nitrous oxide observed at Hateruma monitoring station – Tohjima et al. (2000)“In situ measurement of atmospheric nitrous oxide (N2O) has been carried out at Hateruma monitoring station (lat 24°03′N, long 123°48′E) since March 1996 by the National Institute for Environmental Studies (NIES). A fully automated gas chromatograph equipped with an electron capture detector (ECD) measures the N2O concentrations at a frequency of 3 air samples per hour. Details of the experimental methods and procedures are presented in this paper. The N2O concentrations observed from March 1996 to February 1999 increased at an average rate of 0.64 ppb/yr. The observed data also suggest that there is a weak annual cycle of N2O concentration, increasing in autumn and winter and decreasing in spring and summer, with a peak-to-peak amplitude of at most 0.3 ppb.”

Atmospheric Emissions and Trends of Nitrous Oxide Deduced From 10 Years of ALE–GAGE Data – Prinn et al. (1990)“We present and interpret long-term measurements of the chemically and radiatively important trace gas nitrous oxide (N2O) obtained during the Atmospheric Lifetime Experiment (ALE) and its successor the Global Atmospheric Gases Experiment (GAGE). The ALE/GAGE data for N2O comprise over 110,000 individual calibrated real-time air analyses carried out over a 10-year (July 1978–June 1988) time period. These measurements indicate that the average concentration in the northern hemisphere is persistently 0.75 ± 0.16 ppbv higher than in the southern hemisphere and that the global average linear trend in N2O lies in the range from 0.25 to 0.31% yr−1, with the latter result contingent on certain assumptions about the long-term stability of the calibration gases used in the experiment. … The measured trends and latitudinal distributions are consistent with the hypothesis that stratospheric photodissociation is the major atmospheric sink for N2O, but they do not support the hypothesis that the temporal N2O increase is caused solely by increases in anthropogenic N2O emissions associated with fossil fuel combustion. Instead, the cause for the N2O trend appears to be a combination of a growing tropical source (probably resulting from tropical land disturbance) and a growing northern mid-latitude source (probably resulting from a combination of fertilizer use and fossil fuel combustion).”

Increase and seasonal cycles of nitrous oxide in the earth’s atmosphere – Khalil & Rasmussen (1983)“Based on about nine thousand ground-level measurements at Cape Meares, Oregon (45° N), and Cape Grim, Tasmania (42° S), spanning three years, it is shown that nitrous oxide (N2O) is increasing at about 0.9 p.p.b. yr−1 (0.6, 1.1) in the northern hemisphere, and at 0.7 p.p.b. yr−1 (±0.2 p.p.b. yr−1) in the southern hemisphere. It is also shown that N2O concentrations vary with the season. On average, northern hemisphere concentrations are 0.8 p.p.b.v. higher during April, May, and June compared to the rest of the year, and southern hemisphere concentrations are about 0.5 p.p.b.v. lower during March, April, and May compared to the rest of the year. Based on the existing estimates of natural and anthropogenic sources of N2O, the increase is explained by a sizeable anthropogenically-controlled land-based source. Mass-balance calculations also indicate that a natural land-based source, peaking in spring, would explain the main features of the observed seasonal cycle.”

Historic concentration

Glacial–interglacial and millennial-scale variations in the atmospheric nitrous oxide concentration during the last 800,000 years – Schilt et al. (2010)“We present records of atmospheric nitrous oxide obtained from the ice cores of the European Project for Ice Coring in Antarctica (EPICA) Dome C and Dronning Maud Land sites shedding light on the concentration of this greenhouse gas on glacial–interglacial and millennial time scales. The extended EPICA Dome C record covers now all interglacials of the last 800,000 years and reveals nitrous oxide variations in concert with climate. Highest mean interglacial nitrous oxide concentrations of 280 parts per billion by volume are observed during the interglacial corresponding to Marine Isotope Stage 11 around 400,000 years before present, at the same time when carbon dioxide and methane reach maximum mean interglacial concentrations. The temperature reconstruction at Dome C indicates colder interglacials between 800,000 and 440,000 years before present compared to the interglacials of the last 440,000 years. In contrast to carbon dioxide and methane, which both respond with lower concentrations at lower temperatures, nitrous oxide shows mean interglacial concentrations of 4–19 parts per billion by volume higher than the preindustrial Holocene value during the interglacials corresponding to Marine Isotope Stage 9–19. At the end of most interglacials, nitrous oxide remains substantially longer on interglacial levels than methane. Nevertheless, nitrous oxide shows millennial-scale variations at the same time as methane throughout the last 800,000 years. We suggest that these millennial-scale variations have been driven by a similar mechanism as the Dansgaard/Oeschger events known from the last glacial. Our data lead to the hypothesis that emissions from the low latitudes drive past variations of the atmospheric nitrous oxide concentration.” [Full text]

Law Dome CO2, CH4 and N2O ice core records extended to 2000 years BP – MacFarling Meure et al. (2006)“New measurements of atmospheric greenhouse gas concentrations in ice from Law Dome, Antarctica reproduce published Law Dome CO2 and CH4 records, extend them back to 2000 years BP, and include N2O. … Major increases in CO2, CH4 and N2O concentrations during the past 200 years followed a period of relative stability beforehand. Decadal variations during the industrial period include the stabilization of CO2 and slowing of CH4 and N2O growth in the 1940s and 1950s. Variations of up to 10 ppm CO2, 40 ppb CH4 and 10 ppb N2O occurred throughout the preindustrial period.”

Ice Core Records of Atmospheric N2O Covering the Last 106,000 Years – Sowers et al. (2003)“Here, we present a 106,000-year record of atmospheric nitrous oxide (N2O) along with corresponding isotopic records spanning the last 30,000 years, which together suggest minimal changes in the ratio of marine to terrestrial N2O production. During the last glacial termination, both marine and oceanic N2O emissions increased by 40 ± 8%. We speculate that our records do not support those hypotheses that invoke enhanced export production to explain low carbon dioxide values during glacial periods.

High-resolution Holocene N2O ice core record and its relationship with CH4 and CO2 – Flückiger et al. (2002)“Little is known, however, about possible N2O variations during the more stable climate of the present interglacial (Holocene) spanning the last 11 thousand years. Here we fill this gap with a high-resolution N2O record measured along the European Project for Ice Coring in Antarctica (EPICA) Dome C Antarctic ice core. On the same ice we obtained high-resolution methane and carbon dioxide records. This provides the unique opportunity to compare variations of the three most important greenhouse gases (after water vapor) without any uncertainty in their relative timing. The CO2 and CH4 records are in good agreement with previous measurements on other ice cores. The N2O concentration started to decrease in the early Holocene and reached minimum values around 8 ka (<260 ppbv) before a slow increase to its preindustrial concentration of ~265 ppbv." [Full text]

Variations in Atmospheric N2O Concentration During Abrupt Climatic Changes – Flückiger et al. (1999)“Records measured along two ice cores from Summit in Central Greenland provide information about variations in atmospheric N2O concentration in the past. The record covering the past millennium reduces the uncertainty regarding the preindustrial concentration. Records covering the last glacial-interglacial transition and a fast climatic change during the last ice age show that the N2O concentration changed in parallel with fast temperature variations in the Northern Hemisphere.”

Increase in the atmospheric nitrous oxide concentration during the last 250 years – Machida et al. (1995)“In order to estimate the concentrations of atmospheric nitrous oxide (N2O) during the last 250 years, air samples were extracted from an Antarctic ice core, H15, using a dry extraction system and were then analyzed with a precision of ±2 ppbv. The results obtained were clearly less scattered and much tighter than those of the previous studies. Our data showed that the concentrations of atmospheric N2O in the 18th century were about 276 ppbv on average. It was also obvious that the N2O concentration began to increase in the mid‐19th century and reached approximately 293 ppbv around 1965, the trend of the concentration increase correlating quite well with the direct atmospheric measurements at the South Pole. Such an increase in the atmospheric N2O concentration is thought to be of anthropogenic origin.”

Nitrous oxide in the Earth’s atmosphere – Badr & Probert (1992)“Nitrous oxide (N2O) is an important atmospheric trace gas. Changes in the concentration of N2O in the atmosphere have evoked considerable interest because of its role in (i) regulating stratospheric ozone levels, and (ii) contributing to the atmospheric greenhouse phenomenon. The global concentration of N2O in the atmosphere has been rising since the start of the Industrial Revolution, before which the concentration was almost constant at about 280–290 ppbv. In AD 1990, it reached about 310 ppbv and is rising at a rate of 0·5–1·1 ppbv (i.e. 0·2–0·3%) per year. In this paper, the history of N2O in the Earth’s atmosphere, together with its latitudinal and altitudinal distributions, and seasonal oscillations, are described.”

N2O measurements of air extracted from antarctic ice cores: Implication on atmospheric N2O back to the last glacial-interglacial transition – Zardini et al. (1989)“A method has been developed for determining the N2O concentrations of air bubbles trapped in ice cores. The air is removed by cutting ice samples of about 45 cm3 with a rotating knife, under pure nitrogen. About 2 cm3 of the gas extracted from the ice is analyzed. The N2O concentrations are measured by gas chromatography, using electron capture detection with a detection limit of approximately 1 ppbv. The accuracy of the analysis is lower than 6%. This method has been used to analyze 34 Antarctic ice samples. Twelve air samples are from the D57 core and date approximately from AD 1600 and 1900. Data indicate a concentration of about 270 ppbv approximately 400 years ago, and of about 293 ppbv for the beginning of the 20th Century. The other samples have been taken from the Dome C core and date back to the time period extending from the Holocene to the Last Glacial Maximum. The results obtained for the Holocene period are in very good agreement with the concentrations measured for the pre-industrial time from the D57 core and indicate that, during the Holocene period, atmospheric N2O mixing ratios may have remained fairly constant. The value observed during the last climatic transition suggest a slight increase in the N2O concentrations when the climate was warming up.”

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Recently, I showed briefly a simple observational proof that greenhouse effect exists using a paper by Ellingson & Wiscombe (1996). Now I will present a similar paper that deepens the proof and shows more clearly how different greenhouse gases really are greenhouse gases. I’ll highlight the carbon dioxide related issues in their paper.

Walden et al. (1998) studied the downward longwave radiation spectrum in Antarctica. Their study covers only a single year so this is not about how the increase in greenhouse gases affects. They measured the downward longwave radiation spectrum coming from atmosphere to the surface during the year (usually in every 12 hours) and then selected three measurements from clear-sky days for comparison with the results of a line-by-line radiative transfer model.

First they described why Antarctica is a good place for this kind of study:

Since the atmosphere is so cold and dry (<1 mm of precipitable water), the overlap of the emission spectrum of water vapor with that of other gases is greatly reduced. Therefore the spectral signatures of other important infrared emitters, namely, CO2, O3, CH4, and N2O, are quite distinct. In addition, the low atmospheric temperatures provide an extreme test case for testing models

Spectral overlapping is a consideration here because they are using a moderate resolution (about 1 cm-1) in their spectral analysis. They went on further describing their measurements and the equipment used and their calibration. They also discussed the uncertainties in the measurements thoroughly.

They then presented the measured spectra in similar style than was shown in Ellingson & Wiscombe (1996). They proceeded to produce their model results. The models were controlled with actual measurements of atmospheric consituents (water vapour, carbon dioxide, etc.). The model is used here because it represents our theories which are based on numerous experiments in laboratories and in the atmosphere. They then performed the comparison between the model results and the measurements. Figure 1 shows their Figure 11 where total spectral radiance from their model is compared to measured spectral radiance.

The upper panel of Figure 1 shows the spectral radiance and the lower panel shows the difference of measured and modelled spectrum. The overall match is excellent and there’s no way you could get this match by chance so this already shows that different greenhouse gases really are producing a greenhouse effect just as our theories predict. Walden et al. didn’t stop there. Next they showed the details of how the measured spectral bands of different greenhouse gases compare with model results. The comparison of carbon dioxide is shown here in Figure 2 (which is the upper panel of their figure 13).

The match between the modelled and measured carbon dioxide spectral band is also excellent, even the minor details track each other well except for couple of places of slight difference. If there wouldn’t be greenhouse effect from carbon dioxide or if water vapour would be masking its effect, this match should then be accidental. I see no chance for that, so this seems to be a simple observational proof that carbon dioxide produces a greenhouse effect just as our theories predict.

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This is a list of papers on late Pliocene cooling event that happened about 3 million years ago and caused the glaciation of the northern hemisphere. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Late Pliocene Greenland glaciation controlled by a decline in atmospheric CO2 levels – Lunt et al. (2008)“Several hypotheses have been proposed to explain this increase in Northern Hemisphere glaciation during the Late Pliocene. Here we use a fully coupled atmosphere–ocean general circulation model and an ice-sheet model to assess the impact of the proposed driving mechanisms for glaciation and the influence of orbital variations on the development of the Greenland ice sheet in particular. We find that Greenland glaciation is mainly controlled by a decrease in atmospheric carbon dioxide during the Late Pliocene. By contrast, our model results suggest that climatic shifts associated with the tectonically driven closure of the Panama seaway, with the termination of a permanent El Niño state or with tectonic uplift are not large enough to contribute significantly to the growth of the Greenland ice sheet; moreover, we find that none of these processes acted as a priming mechanism for glacial inception triggered by variations in the Earth’s orbit.”[Full text]

Slow dynamics of the Northern Hemisphere glaciation – Mudelsee & Raymo (2005)“We use 45 δ18O records from benthic and planktonic foraminifera and globally distributed sites to reconstruct the dynamics of NHG initiation. We compare δ18O amplitudes with those of temperature proxy records and estimate a global ice volume–related increase of 0.4‰, equivalent to an overall sea level lowering of 43 m. We find the NHG started significantly earlier than previously assumed, as early as 3.6 Ma, and ended at 2.4 Ma. This long-term increase points to slow, tectonic forcing such as closing of ocean gateways or mountain building as the root cause of the NHG.”[Full text]

Final closure of Panama and the onset of northern hemisphere glaciation – Bartoli et al. (2005)“In contrast, our new submillennial-scale paleoceanographic records from the Pliocene North Atlantic suggest a far more precise timing and forcing for the initiation of northern hemisphere glaciation (NHG), since it was linked to a 2–3 °C surface water warming during warm stages from 2.95 to 2.82 Ma. These records support previous models [G.H. Haug, R. Tiedemann, Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation, Nature 393 (1998) 673–676. [2]] claiming that the final closure of the Panama Isthmus (3.0– 2.5 Ma [J. Groeneveld S. Steph, R. Tiedemann, D. Nürnberg, D. Garbe-Schönberg, The final closure of the Central American Seaway, Geology, in prep. [3]]) induced an increased poleward salt and heat transport. Associated strengthening of North Atlantic Thermohaline Circulation and in turn, an intensified moisture supply to northern high latitudes resulted in the build-up of NHG, finally culminating in the great, irreversible “climate crash” at marine isotope stage G6 (2.74 Ma). In summary, there was a two-step threshold mechanism that marked the onset of NHG with glacial-to-interglacial cycles quasi-persistent until today.”[Full text]

Regional climate shifts caused by gradual global cooling in the Pliocene epoch – Ravelo et al. (2004)“Here we compare climate records from high latitudes, subtropical regions and the tropics, indicating that the onset of large glacial/interglacial cycles did not coincide with a specific climate reorganization event at lower latitudes. The regional differences in the timing of cooling imply that global cooling was a gradual process, rather than the response to a single threshold or episodic event as previously suggested. We also find that high-latitude climate sensitivity to variations in solar heating increased gradually, culminating after cool tropical and subtropical upwelling conditions were established two million years ago.”[Full text]

Role of tropics in changing the response to Milankovich forcing some three million years ago – Philander & Fedorov (2003)“Throughout the Cenozoic the Earth experienced global cooling that led to the appearance of continental glaciers in high northern latitudes around 3 Ma ago. At approximately the same time, cold surface waters first appeared in regions that today have intense oceanic upwelling: the eastern equatorial Pacific and the coastal zones of southwestern Africa and California. There was furthermore a significant change in the Earth’s response to Milankovich forcing: obliquity signals became large, but those associated with precession and eccentricity remained the same. The latter change in the Earth’s response can be explained by hypothesizing that the global cooling during the Cenozoic affected the thermal structure of the ocean; it caused a gradual shoaling of the thermocline. Around 3 Ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions. This brought into play feedbacks involving ocean-atmosphere interactions of the type associated with El Niño and also mechanisms by which high-latitude surface conditions can influence the depth of the tropical thermocline. Those feedbacks and mechanisms can account for the amplification of the Earth’s response to periodic variations in obliquity (at a period of 41K) without altering the response to Milankovich forcing at periods of 100,000 and 23,000 years. This hypothesis is testable. If correct, then in the tropics and subtropics the response to obliquity variations is in phase with, and corresponds to, El Niño conditions when tilt is large and La Niña conditions when tilt is small.”[Full text]

The contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation – Maslin et al. (1998)“In this study, we reconstruct the timing of the onset of Northern Hemisphere glaciation. This began in the late Miocene with a significant build-up of ice on Southern Greenland. However, progressive intensification of glaciation did not begin until 3.5-3 Ma, when the Greenland ice sheet expanded to include Northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia were glaciated at approximately 2.74 Ma, 40 ka before the glaciation of Alaska (2.70 Ma) and about 200 ka before significant glaciation of the North East American continent (2.54 Ma). We also review the suggested causes of Northern Hemisphere glaciation. Tectonic changes, such as the uplift of the Himalayan and Tibetan Plateau, the deepening of the Bering Strait and the emergence of the Panama Isthmus, are too gradual to account entirely for the speed of Northern Hemisphere glaciation. We, therefore, postulate that tectonic changes may have brought global climate to a critical threshold, but the relatively rapid variations in the Earth’s orbital parameters and thus insolation, triggered the intensification of Northern Hemisphere glaciation. This theory is supported by computer simulations, which despite the relative simplicity of the model and the approximation of some factors (e.g. using a linear carbon dioxide scenario, neglecting the geographical difference between the Pliocene and the present) suggest that it is possible to build-up Northern Hemisphere ice sheets, between 2.75 and 2.55 Ma, by varying only the insolation controlled by the orbital parameters.”[Full text]

The progressive intensification of northern hemisphere glaciation as seen from the North Pacific – Maslin et al. (1996)“Ocean Drilling Project (ODP) site 882 (50°22′N, 167°36′E) provides the first high-resolution GRAPE density, magnetic susceptibility, carbonate, opal and foraminifera (planktonic and benthic) stable isotopes records between 3.2 and 2.4 Ma in the Northwest Pacific. We observed a dramatic increase in ice rafting debris at site 882 at 2.75 Ma, which is coeval with that found in the Norwegian Sea, suggesting that the Eurasian Arctic and Northeast Asia were significantly glaciated from 2.75 Ma onwards. Prior to 2.75 Ma planktonic foraminifera δ18O records indicate a warming or freshening trend of 4°C or 2‰ over 80 ka. If this is interpreted as a warm pre-glacial Pliocene North Pacific, it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet. The dramatic drop in sea surface temperatures (SST>7.5°C) at 2.75 Ma ended this suggested period of enhanced SST and thus the proposed moisture pump. Moreover, at 2.79 and 2.73 Ma opal mass accumulation rates (MAR) decrease in two steps by five fold and is accompanied by a more gradual long-term decrease in CaCO3 MARs. Evidence from the Southern Ocean (ODP site 704) indicates that just prior to 2.6 Ma there is a massive increase in opal MARs, the opposite to what is found in the North Pacific. This indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget, possibly caused by changes in deep ocean circulation. The initiation of northern hemisphere glaciation occurred in the late Miocene with a significant build up of ice on southern Greenland. However, the progressive intensification did not occur until 3.5–3 Ma when the Greenland ice sheet expanded to include northern Greenland. Following this stage we suggest that the Eurasian Arctic and Northeast Asia glaciated at 2.75 Ma, approximately 100 ka before the glaciation of Alaska (2.65 Ma) and 200 ka before the glaciation of the North East American continent (2.54 Ma).”

The Initiation of Northern Hemisphere Glaciation – Raymo (1994) A review article. “In this paper, the climate transition from the warm mid-Pliocene (around 3.2 Ma) to the onset of northern hemisphere ice ages around 2.4 Ma is examined. Evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe.”[Full text]

Tectonic forcing of late Cenozoic climate – Raymo & Ruddiman (1992)“Global cooling in the Cenozoic, which led to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan plateau and the positive feedbacks initiated by this event. In particular, tectonically driven increases in chemical weathering may have resulted in a decrease of atmospheric C02 concentration over the past 40 Myr.”[Full text]

The cause of the Late Cenozoic Northern Hemisphere glaciations: a climate change enigma – Hay (1992)“The ultimate cause of the onset of glaciations remains elusive, but in the case of northem hemisphere glaciation it is probable that several factors acted in combination. General global cooling resulted from reduction of atmospheric C02 by weathering of silicate rocks exposed by erosion of late Cenozoic uplifts. Uplifts in south Asia, southwestern North America and Scandinavia occurred at distances appropriate for the generation of quasi-permanent Rossby waves in the atmosphere. The resulting winds, given suitable moisture sources, were favourable for causing large-scale precipitation at mid-latitudes on the northern continents. Moisture sources were provided by the closure of the Central American isthmus. Gulf Stream flow increased, carrying warm subtropical waters to high latitudes. The Denmark Strait deepened permitting greater outflow of deep water from the Norwegian-Greenland Sea. The relative importance of each of these factors should be investigated by additional atmospheric and ocean climate model sensitivity studies.”

Global Wind-Induced Change of Deep-Sea Sediment Budgets, New Ocean Production and CO2 Reservoirs ca. 3.3-2.35 Ma BP – Sarnthein & Fenner (1988)“The late Pliocene phase of large-scale climatic deterioration about 3.2-2.4 Ma BP is well documented in a number of (benthic) δ18O records. To test the global implications of this event, we have mapped the distribution patterns of various sediment variables in the Pacific and Atlantic Oceans during two time slices, 3.4-3.18 and 2.43-2.33 Ma BP. The changes of bulk sedimentation and bulk sediment accumulation rates are largely explained by the variations of CaCO3-accumulation rates (and the accumulation rates of the complementary siliciclastic sediment fraction near continents in higher latitudes). During the late Pliocene, the CaCO3-accumulation rate increased along the equatorial Pacific and Atlantic and in the northeastern Atlantic, but decreased elsewhere. The accumulation rate of organic carbon (Corg) and net palaeoproductivity also increased below the high-productivity belts along the equator and the eastern continental margins. From these patterns we may conclude that (trade-) wind-induced upwelling zones and upwelling productivity were much enhanced during that time. This change led to an increased transfer of CO2 from the surface ocean to the ocean deep water and to a reduction of evaporation, which resulted in an aridification of the Saharan desert belt as depicted in the dust sediments off northwest Africa.”

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This is a list of papers on atmospheric methane concentration measurements. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Modern methane concentration

Continuous measurements of methane from a tower network over Siberia – Sasakawa et al. (2010)“We have been conducting continuous measurements of CH4 concentration from an expanding network of towers (JR-STATION: Japan–Russia Siberian Tall Tower Inland Observation Network) located in taiga, steppe, and wetland biomes of Siberia since 2004. High daytime means (>2000 ppb) observed simultaneously at several towers during winter, together with in-situ weather data and NCEP/NCAR reanalysis data, indicate that high pressure systems caused CH4 accumulation at sub-continental scale due to the widespread formation of an inversion layer. Daytime means sometimes exceeded 2000 ppb, particularly in the summer of 2007 when temperature and precipitation rates were anomalously high over West Siberia, which implies that CH4 emission from wetlands were exceptionally high in 2007. Many hot spots detected by MODIS in the summer of 2007 illustrate that the contribution of biomass burning also cannot be neglected. Daytime mean CH4 concentrations from the Siberian tower sites were generally higher than CH4 values reported at NOAA coastal sites in the same latitudinal zone, and the difference in concentrations between two sets of sites was reproduced with a coupled Eulerian–Lagrangian transport model. Simulations of emissions from different CH4 sources suggested that the major contributor to variation switched from wetlands during summer to fossil fuel during winter.”

Seasonal cycles of mixing ratio and 13C in atmospheric methane at Suva, Fiji – Lowe et al. (2004)“A series of clean air samples has been collected at a coastal site near Suva, Fiji (18°08′S, 178°26′E) by researchers at the University of the South Pacific. These samples, covering the period 1994 to mid-2002, have been analyzed for methane mixing ratio and δ13C and provide the first ever time series of these species reported for this part of the tropical South Pacific. The data show large variability when compared to similar time series of the same species measured farther south in the extratropical Pacific. In particular, summer variability at the Fiji site is high, especially through La Niña conditions.”

Tropospheric methane retrieved from ground-based near-IR solar absorption spectra – Washenfelder et al. (2003)“High-resolution near-infrared solar absorption spectra recorded between 1977 and 1995 at the Kitt Peak National Solar Observatory are analyzed to retrieve column abundances of methane (CH4), hydrogen fluoride (HF), and oxygen (O2). Employing a stratospheric “slope equilibrium” relationship between CH4 and HF, the varying contribution of stratospheric CH4 to the total column is inferred. Variations in the CH4 column due to changes in surface pressure are determined from the O2 column abundances. By this technique, CH4 tropospheric volume mixing ratios are determined with a precision of ~0.5%. These display behavior similar to Mauna Loa in situ surface measurements, with a seasonal peak-to-peak amplitude of approximately 30 ppbv and a nearly linear increase between 1977 and 1983 of 18.0 ± 0.8 ppbv yr−1, slowing significantly after 1990.”[Full text]

Atmospheric methane levels off: Temporary pause or a new steady-state? – Dlugokencky et al. (2003)“The globally-averaged atmospheric methane abundance determined from an extensive network of surface air sampling sites was constant at ~1751 ppb from 1999 through 2002. Assuming that the methane lifetime has been constant, this implies that during this 4-year period the global methane budget has been at steady state. We also observed a significant decrease in the difference between northern and southern polar zonal annual averages of CH4 from 1991 to 1992. … Based on current knowledge of the global methane budget and how it has changed with time, it is not possible to tell if the atmospheric methane burden has peaked, or if we are only observing a persistent, but temporary pause in its increase.”[Full text]

In situ measurements of atmospheric methane at GAGE/AGAGE sites during 1985–2000 and resulting source inferences – Cunnold et al. (2002)“Continuous measurements of methane since 1986 at the Global Atmospherics Gases Experiment/Advanced Global Atmospherics Gases Experiment (GAGE/AGAGE) surface sites are described. … The measurements exhibit good agreement with coincident measurements of air samples from the same locations analyzed by Climate Monitoring and Diagnostics Laboratory (CMDL) except for differences of approximately 5 ppb before 1989 (GAGE lower) and about 4 ppb from 1991 to 1995 (GAGE higher). … The measurements combined with a 12-box atmospheric model and an assumed atmospheric lifetime of 9.1 years indicates net annual emissions (emissions minus soil sinks) of 545 Tg CH4 with a variability of only ±20 Tg from 1985 to 1997 but an increase in the emissions in 1998 of 37 ± 10 Tg.”

The growth rate and distribution of atmospheric methane – Dlugokencky et al. (1994)“Methane was measured in air samples collected approximately weekly from a globally distributed network of sites from 1983 to 1992. Sites range in latitude from 90°S to 82°N. … The data reveal a strong north‐south gradient in methane with an annual mean difference of about 140 ppb between the northernmost and southernmost sampling sites. … Seasonal cycle amplitudes in the high north are about twice those observed in the high southern hemisphere. … The average increase in the globally averaged methane mixing ratio over the period of these measurements is (11.1 ± 0.2) ppb yr−1. Globally, the growth rate for methane decreased from approximately 13.5 ppb yr−1 in 1983 to about 9.3 ppb yr−1 in 1991. The growth rate of methane in the northern hemisphere during 1992 was near zero. Various possibilities for the long‐term, slow decrease in the methane growth rate over the last decade and the rapid change in growth rate in the northern hemisphere in 1992 are given. The most likely explanation is a change in a methane source influenced directly by human activities, such as fossil fuel production.”

Atmospheric methane data for the period 1986-1988 from the NOAA /CMDL global cooperative flask sampling network – Lang et al. (1990)“The memorandum builds on previous work (Lang et al., 1987) to extend by three years the record of atmospheric methane measurements made through the NOAA/CMDL cooperative flask sampling network. The format of the data presentations given here follows very closely that used by Lang et al., (1990). Details of the flask sampling methods and the analytical and calibrational procedures are given. Results from individual flask samples are both tabulated and plotted. Monthly average methane concentrations at each site are also tabulated.”

Atmospheric methane data for the period 1983-1985 from the NOAA /GMCC global cooperative flask sampling network – Lang et al. (1990)“Details of relevant aspects of the NOAA Global Monitoring for Climate Change (GMCC) program to measure atmospheric methane concentrations through its global, cooperative, flask sampling network are discussed. These aspects include the history of the development of the program; details of the sampling network; the flasks and the flask sampling methods; the analytical instrumentation and methods; and the calibration gases and methods. The data from individual flask samples are tabulated, as are the monthly average methane concentrations. Through adequate documentation it is more likely that the full value of these methane measurements will be realized in long-term studies of the greenhouse effect and climate change.”

World-wide increase in tropospheric methane, 1978–1983 – Blake & Rowland (1986)“Tropospheric concentrations of methane in remote locations have averaged a yearly world-wide increase of 0.018±0.002 parts per million by volume (ppmv) during the period from January 1978 to December 1983. The concentrations in the north temperate zone are always greater than those in the south temperate zone by 7±1% because the major methane sources are all predominantly located in the northern hemisphere. The average world-wide tropospheric concentration of methane in dry air was 1.625 ppmv at the end of 1983, measured against an NBS standard certified as 0.97 ppmv (but with an accuracy of only ±1%).”

Sources, Sinks, and Seasonal Cycles of Atmospheric Methane – Khalil & Rasmussen (1983)“The extensive set of self consistent measurements of methane are reported and analyzed showing that methane has increased during the last 3–4 years at rates of 1–1.9% per year all over the world at sites ranging from inside the arctic circle to the south pole. Observational results are used to estimate the sources, sinks, seasonal cycles of CH4, and the effects of human activities on its atmospheric abundance.”

Atmospheric Methane (CH4): Trends and Seasonal Cycles – Rasmussen & Khalil (1981)“On the basis of 22 months of almost continuous, automated, GC/FID measurements of atmospheric CH4 at Cape Meares (45°N), we show that the concentration of CH4 is increasing at about 2% per yr (±0.5% yr−1). The data also revealed stable seasonal cycles with peak concentrations in October and minimum concentrations in July. The magnitude of the seasonal variations during these months is about ±20 ppbv from the average (∼±1.2%).”

Methane concentration in the past

Orbital and millennial-scale features of atmospheric CH4 over the past 800,000 years – Loulergue et al. (2008)“Here we present a detailed atmospheric methane record from the EPICA Dome C ice core that extends the history of this greenhouse gas to 800,000 yr before present. The average time resolution of the new data is 380 yr and permits the identification of orbital and millennial-scale features. Spectral analyses indicate that the long-term variability in atmospheric methane levels is dominated by 100,000 yr glacial–interglacial cycles up to 400,000 yr ago with an increasing contribution of the precessional component during the four more recent climatic cycles.”[Full text]

Atmospheric Methane and Nitrous Oxide of the Late Pleistocene from Antarctic Ice Cores – Spahni et al. (2005)“The European Project for Ice Coring in Antarctica Dome C ice core enables us to extend existing records of atmospheric methane (CH4) and nitrous oxide (N2O) back to 650,000 years before the present. A combined record of CH4 measured along the Dome C and the Vostok ice cores demonstrates, within the resolution of our measurements, that preindustrial concentrations over Antarctica have not exceeded 773 ± 15 ppbv (parts per billion by volume) during the past 650,000 years. Before 420,000 years ago, when interglacials were cooler, maximum CH4 concentrations were only about 600 ppbv, similar to lower Holocene values.”[supplementary information]

Variations in atmospheric methane concentration during the Holocene epoch – Blunier et al. (2002)“Here we present a continuous, high-resolution record of atmospheric methane from 8,000 to 1,000 yr BP, from the GRIP ice core in central Greenland. Unlike most other climate proxies from ice cores (such as oxygen isotope composition and electrical conductivity), methane concentrations show significant variations—up to 15%—during the Holocene. We have proposed1 that variations in the hydrological cycle at low latitudes are the dominant control on past levels of atmospheric methane. This is now supported by the observation that the lowest methane concentrations in our new record occur in the mid-Holocene, when many tropical lakes dried up. The concentration increases during the Late Holocene, probably owing to an increasing contribution from northern wetlands.”

Atmospheric methane between 1000 A.D. and present: Evidence of anthropogenic emissions and climatic variability – Etheridge et al. (1998)“Atmospheric methane mixing ratios from 1000 A.D. to present are measured in three Antarctic ice cores, two Greenland ice cores, the Antarctic firn layer, and archived air from Tasmania, Australia. … From 1000 to 1800 A.D. the global mean methane mixing ratio averaged 695 ppb and varied about 40 ppb, contemporaneous with climatic variations. Interpolar (N-S) differences varied between 24 and 58 ppb. The industrial period is marked by high methane growth rates from 1945 to 1990, peaking at about 17 ppb yr−1 in 1981 and decreasing significantly since.”

Rapid Variations in Atmospheric Methane Concentration During the Past 110,000 Years – Brook et al. (1996)“A methane record from the GISP2 ice core reveals that millennial-scale variations in atmospheric methane concentration characterized much of the past 110,00 years. As previously observed in a shorter record from central Greenland, abrupt concentration shifts of about 50 to 300 parts per billion by volume were coeval with most of the interstadial warming events (better known as Dansgaard-Oeschger events) recorded in the GISP2 ice core throughout the last glacial period. The magnitude of the rapid concentration shifts varied on a longer time scale in a manner consistent with variations in Northern Hemisphere summer insolation, which suggests that insolation may have modulated the effects of interstadial climate change on the terrestrial biosphere.”

Changes in tropospheric methane between 1841 and 1978 from a high accumulation-rate Antarctic ice core – Etheridge et al. (1992)“To determine in detail how the concentration of tropospheric methane has changed from preindustrial until recent times, an ice core with remarkably fine air-age resolution was investigated. The core, called DE08, contains air from as recent as 1978 with an age resolution (80% air-age distribution width) of about 14 years. … Methane concentrations in the DE08 record increased from 823 parts per billion by volume (ppbv, in dry air) in 1841 to 1481 ppbv in 1978. The measurement precision was ± 22 ppbv (1σ). The similarity of the methane records from the DE08 ice core and from Cape Grim, Tasmania implies that there was insignificant modification during the enclosure of air in the ice or during its recovery and analysis. Methane concentrations in the period from 1951 to 1978, which were previously estimated from sporadic and inferred data, are particularly well defined in this core. The DE08 record shows that methane growth rates have generally increased since the onset of the industrial revolution to a level of 14 ppbv year−1 (about 1% per year) by the 1970s. The exception was between about 1920-1945 when the growth rate stabilised at about 5 ppbv year−1.”

Ice-core record of atmospheric methane over the past 160,000 years – Chappellaz et al. (1990)“Methane measurements along the Vostok ice core are reported which reveal strong variations of past CH4 concentrations in the 350-650 ppbv range, well below the present atmospheric conditions. These variations are well-correlated with climate change deduced from the isotopic composition of the Vostok ice core. Spectral analysis of the record indicates periodicities close to those of orbital variations. These CH4 changes are interpreted here as being the result of fluctuations in wetland areas induced by climate changes. It is suggested that the participation of CH4 and associated chemical feedbacks to warming during deglaciations represents about 30 percent of that due to CO2.”

Atmospheric Methane in the Recent and Ancient Atmospheres: Concentrations, Trends, and Interhemispheric Gradient – Rasmussen & Khalil (1984)“Upon analyzing some 80 ice core samples from the polar regions we found that the concentration of methane 250 years ago and earlier was only 700 (±30) ppbv, or about 45% of present levels. A rapid and significant increase of atmospheric methane started about 150 years ago. The rate of increase has escalated since then and is about 1.3%/yr at present. We also found that the concentration of methane in the atmosphere 250 years ago and earlier, when methane was not increasing, was 10% (±4%) higher in the Arctic as compared to the Antarctic. This finding is consistent with the expected ratio of about 1.07–1.11 obtained from a global mass balance model and the primarily land-based natural sources of methane, estimated to be about 280 Tg/yr, which may have been the only sources several hundred years ago, when human activities did not contribute significantly to the global methane cycle.”

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This is a list of papers presenting the theoretical work on the CO2 absorption properties. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (December 23, 2010): Stull et al. (1964) added.

Collision-induced absorption by CO2 in the far infrared: Analysis of leading-order moments and interpretation of the experiment – Kouzov & Chrysos (2009)“The diagrammatic theory, developed recently by the authors [Phys. Rev. A 74, 012732 (2006)], is applied to binary collision-induced properties, with emphasis on induced dipole moments. Assuming rototranslational dynamics to be classical and using irreducible spherical tensor formalism, exact analytical formulas are worked out for the two leading order spectral moments of a collision-induced band by two interacting linear molecules. The formulas are applied to the far infrared absorption by CO2-CO2, and permit interpretation of the experiment. This study provides evidence of the adequacy of the electrostatic induction mechanism, provided that hitherto missing vibrational terms of static polarizability are considered.”

Exact Low-Order Classical Moments in Collision-Induced Bands by Linear Rotors: CO2-CO2 – Chrysos et al. (2008)“Exact and general analytic expressions are reported for the integrated intensity and the width of collision-induced absorption (CIA) and collision-induced scattering (CIS) bands by gases of centrosymmetric linear molecules. These expressions provide significant insight and allow assignment of partial second moments to the degrees of freedom of the colliding molecules. The expressions are applied to ambient CO2, whose collisional spectra are reputed to be useful probes for terrestrial and planetary atmospheres. Compelling evidence of the substantial role of hitherto missing polarization and polarizability mechanisms is provided and is in remarkable agreement with experimental observation. Our findings allow the long-overdue simple interpretation of CIA and CIS by CO2-CO2 without the need to resort to short-range interactions to offset the discrepancies between theory and experiment.”

Spectra calculations in central and wing regions of CO2 IR bands between 10 and 20 μm. I: model and laboratory measurements – Niro et al. (2004)“In order to analyze the spectra, a theoretical model based on the energy corrected sudden approximation is proposed which accounts for line-mixing effects within the impact approximation. This approach uses the model and associated parameters built previously to model Q branches (JQSRT 1999;61:153) but extends it by now including all P, Q, and R lines. No adjustable parameters are used and fundamental properties of the collisional relaxation operator are verified by using a renormalization procedure. Comparisons between measured and calculated spectra confirm that neglecting line-mixing (Lorentzian model) leads to an overestimation of absorption by up to three orders of magnitude in the far wings. On the other hand, the proposed approach leads to satisfactory results both in regions dominated by contributions of local lines and in the wing: measured spectra are correctly modeled over a range where absorption varies by more than four orders of magnitude. The largest discrepancies, which appear about 150 cm−1 from the ν2 center, can be due to finite duration of collisions effects or to uncertainties in the experimental determination of very weak absorption.”

Semiclassical modeling of infrared pressure-broadened linewidths: A comparative analysis in CO2–Ar at various temperatures – Buldyreva & Chrysos (2001)“A novel semiclassical approach, which makes use of the exact trajectory implemented within the Robert–Bonamy formalism, is employed for modeling infrared pressure-broadened linewidths. As a prototype, the carbon dioxide molecule perturbed by argon is examined in the temperature range 160–760 K, for which various measurements and computations are available. For a meaningful comparison with previous theoretical works done with both semiclassical and quantum approaches, the ab initio intermolecular potential surface of Parker et al. [J. Chem. Phys. 64, 1668 (1976)] is used. Our values are found to be in agreement with up-to-date experimental data at all temperatures studied.”

A Study of the Radiative Effects of the 9.4- and 10.4-Micron Bands of Carbon Dioxide – Kratz et al. (1991)“The potential radiative impact of the relatively weak 9.4- and 10.4-μm bands of CO2 is investigated. Line-by-line calculations are employed as a standard against which to compare the accuracy of laboratory data, narrow-band models, and broadband models. A comparison of the line-by-line calculations to laboratory data demonstrates that the line-by-line procedure and laboratory data typically yield comparable results; however, there are cases of substantial disagreement between the line-by-line results and the laboratory data. … Clear-sky flux calculations demonstrate that for projected increases of CO2 the impact of the 9.4- and 10.4-μm bands is comparable to that attributed to projected increases of tropospheric ozone.” [Full text]

Approximate Methods for Finding CO2 15-μm Band Transmission in Planetary Atmospheres – Crisp (1986)“The CO2 15-μm band provides an important source of thermal opacity in the atmospheres of Venus, Earth, and Mars. Efficient and accurate methods for finding the transmission in this band are therefore needed before complete, self-consistent physical models of these atmospheres can be developed. In this paper we describe a hierarchy of such methods. The most versatile and accurate of these is an “exact” line-by-line model (Fels and Schwarzkopf, 1981). Other methods described here employ simplifying assumptions about the structure of the 15-μm band which significantly improve their efficiency. … Physical band models based on the Goody (1952) random model compose the first class of approximate methods. These narrow-band models include a general random model and other more efficient techniques that employ the Malkmus (1967) line-strength distribution. Two simple strategies for including Voigt and Doppler line-shape effects are tested. We show that the accuracy of these models at low pressures is very sensitive to the line-strength distribution as well as the line shape. The second class of approximate methods is represented by an exponential wideband model. This physical band model is much more efficient than those described above, since it can be used to find transmission functions for broad sections of the CO2 15-μm band in a single step. When combined with a simple Voigt parameterization, this method produces results almost as accurate as those obtained from the more expensive narrow-band random models. The final class of approximate methods tested here includes the empirical logarithmic wideband models that have been used extensively in climate-modeling studies (Kiehl and Ramanathan, 1983; Pollack et al., 1981). These methods are very efficient, but their range of validity is more limited than that of the other methods tested here. These methods should therefore be used with caution.” [Full text]

The Infrared Transmittance of Carbon Dioxide – Stull et al. (1964)“The infrared transmittance of carbon dioxide has been calculated over a wide range of path lengths, pressures, and temperatures from 500 to 10,000 cm-1. Values of the transmittance are given at intervals of 2.5 cm-1. In addition, transmittance values are also given which have been averaged over larger intervals. All contributing spectral lines whose relative intensity is greater than 10-8 that of the strongest line in any particular band have been included in the calculation. In addition, the contributions from the eight major isotopic species have been included. The calculation of the vibrational energy levels included terms through the third power of the vibrational quantum number and also the effects of Fermi resonance. The final transmittance tables were generated using the quasi-random model of molecular band absorption.” V. Robert Stull, Philip J. Wyatt, and Gilbert N. Plass, Applied Optics, Vol. 3, Issue 2, pp. 243-254 (1964), doi:10.1364/AO.3.000243.

The Temperature Effect on the Absorption of 15 Microns Carbon-Dioxide Band – Sasamori (1959)“Absorptions of a parallel beam of radiation by the 15 μ carbon-dioxide band were calculated for different temperature conditions of the absorbing gas. With use of the results the temperature effect due to the change of the line intensity in the band was examined. It is shown that for short path lengths the temperature effect is governed mainly by the change of the relatively strong lines in the band and that the changes of the weaker lines in the band become important with increasing path length. In the spectral region distant from band center, because of the rapid change of the line intensity, the effect of the temperature change is as appreciable as the pressure effect.” [Full text]

The influence of the 15μ carbon-dioxide band on the atmospheric infra-red cooling rate – Plass (1956)“The upward and downward radiation flux and cooling rate are calculated for the 15μ band of carbon dioxide. Results are obtained for three different carbon-dioxide concentrations from the surface of the earth to 75 km, and for six frequency intervals covering the band. The infra-red absorption measurements of Cloud (1952) are used for calculations, on a high-speed electronic computer, by a method which takes account of the pressure and Doppler broadening, the overlapping of the spectral lines, and the variation of the intensity and half-width of the spectral lines with temperature and pressure. The numerical integration is performed over intervals that are never larger than 1 km and average values over layers are not used. The cooling rate for the present atmospheric carbon-dioxide concentration is greater than 1°C/day from 24 km to 70 km and is greater than 4°C/day from 38 km to 55 km. The sum of the ozone and carbon-dioxide cooling rates is greater than 4°C/day from 33 km to 57 km and agrees reasonably well with the heating due to ozone absorption. The results for different carbon-dioxide concentrations indicate that the average temperature at the surface of the earth would rise by 3.6°C if the carbon-dioxide concentration were doubled and would fall by 3.8°C if the carbon-dioxide concentration were halved, on the assumption that nothing else changed to affect the radiation balance.”

The Effect of Pressure Broadening of Spectral Lines on Atmospheric Temperature – Gilbert & Plass (1950) A paper that shows one reason why carbon dioxide absorption bands are not saturated. “Pressure broadening causes lines in infrared absorption bands to have considerably greater half-widths in the lower layers of a planetary atmosphere than in the upper layers. As a result, radiation emitted upward from the wings of lines in the lower atmosphere is not strongly absorbed by the upper layers. Such radiation is thus free to escape to the cosmic cold.” [For full text, click PDF or GIF links in the abstract page.]

The artificial production of carbon dioxide and its influence on temperature – Callendar (1938)“By fuel combustion man has added about 150,000 million tons of carbon dioxide to the air during the past half century. The author estimates from the best available data that approximately three quarters of this has remained in the atmosphere. The radiation absorption coefficients of carbon dioxide and water vapour are used to show the effect of carbon dioxide on sky radiation. From this the increase in mean temperature, due to the artificial production of carbon dioxide, is estimated to be at the rate of 0.003°C. per year at the present time. The temperature observations a t zoo meteorological stations are used to show that world temperatures have actually increased at an average rate of 0.005°C. per year during the past half century.”

On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground – Arrhenius (1896) There’s no abstract, but I’ll just quote one passage on the absorption calculations. “With the aid of Table III. we may calculate the absorbed fraction of any ray, and then sum up the total absobed heat and determine how great a fraction it is of the total radiation. In this way we find for our example path (air-mass) 1.61. In other words, the total absorbed part of the whole radiation is just as great as if the total radiation traversed the quantities 1.61 of aqueous vapour and of carbonic acid.” [Full text]